Show sample rate pass on Yafaray
I've released YafaRay-E (experimental) v2.0.0, which includes Render Passes, Render Views and, among other things, there is a samplerate pass available that shows the places where the adaptative AA is sampling more pixels. It's not exactly what you showed here, but I hope it's good enough.

You can download it from here:

http://www.yafaray.org/community/forum/viewtopic.php?f=12&amp;t=5132

Best regards.